UNIVERSITY    OF    CALIFORNIA 

COLLEGE    OF    AGRICULTURE 
AGRICULTURAL    EXPERIMENT   STATION 

CIRCULAR  No.  224 
December,  1920 

CONTROL  OF  THE  BROWN  APRICOT  SCALE  AND  THE 
ITALIAN  PEAR  SCALE  ON  DECIDUOUS  FRUIT  TREES 

By  E.  O.  ESSIG 


The  control  of  the  brown  apricot  scale  and  the  Italian  pear  scale 
has  been  so  thoroughly  worked  out  in  practice  that  it  seems  advis- 
able to  make  the  information  serviceable  to  many  fruit  growers  who 
are  not  familiar  with  it.  This  can  best  be  done  by  describing  first 
the  characteristics  of  the  two  insects  separately  and  then  discussing 
the  control  measures  for  both  together. 

THE    BROWN    APRICOT    SCALEi 

The  brown  apricot  scale  is  a  soft,  unarmored  insect  in  which  the 
outside  body  wall  gradually  hardens  until  maturity,  when  it  forms 
a  protecting,  nearly  hemispherical  shell  or  egg-sac  under  which  are 
produced  hundreds  of  small,  oval,  white  eggs.  Upon  hatching,  in 
early  summer,  the  young  insects  crawl  from  beneath  the  old  shell 
and  settle  upon  the  leaves  and  twigs  of  the  current  year's  growth. 
They  grow  slowly  and  in  the  autumn  large  numbers  perish  with  the 
falling  leaves,  but  others  move  to  swell  the  numbers  already  on  the 
twigs,  where  they  remain  through  the  winter  as  small,  elongated, 
brown,  immature  individuals.  With  the  warm  spring  and  early  sum- 
mer days  they  grow  rapidly  and  by  July  and  August  are  mature  and 
produce  eggs,  the  mature  females  dying  soon  afterwards.  During 
growth  the  young  scales  excrete  quantities  of  honey  dew  which 
drops  on  the  leaves,  limbs,  and  fruit  of  the  trees  and  upon  which  the 
black  smut  fungus  thrives.  In  this  way  the  scale  insect  is  directly 
responsible  for  smutting,  the  most  serious  injury  caused  by  this  insect. 
The  males  are  very  minute,  winged  individuals  which  do  not  feed,  so 
that  they  are  not  injurious.  They  mate  with  the  females  when  the 
latter  are  only  about  half  grown.     There  is  but  one  generation  of 

1  Leoanlum  corni  Bouche.     It  is  also  known  as  the  European  fruit  lecanium. 


2  UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION 

the  insect  a  year.  The  females  are  often  attacked  in  great  numbers 
by  a  small  hymenopterous  parasite,  Comys  fasm  Howard.  The  larvae 
of  this  parasite  live  within  the  bodies  of  the  scales,  causing  them 
to  assume  a  very  dark  color  and  eventually  to  dry  up  and  die.  The 
work  of  Comiys  fusca  Howard  is  uncertain  and  sporadic,  so  that  it 
can  be  considered  merely  as  an  adjunct  in  the  control  of  the  scale 
though  sometimes  of  importance. 

The  brown  apricot  scale  is  a  very  general  feeder  attacking  prac- 
tically all  kinds  of  deciduous  fruit  trees,  vines,  and  many  wild  and 
ornamental  trees  and  shrubs.  In  California  it  may  be  found  through- 
out the  length  and  breadth  of  the  state,  but  flourishes  best  in  the 
warmer  valleys,  along  the  coast,  and  in  the  interior. 

THE    ITALIAN    PEAR    SCALE2 

In  contrast  to  the  brown  apricot  scale,  the  Italian  pear  scale  is 
an  armored  scale  in  which  the  small,  oval,  dark  red  body  is  protected 
by  an  elongated  or  nearly  circular  tough  gray  shell  or  scale  which 
averages  about  one-sixteenth  of  an  inch  in  diameter.  The  scales  of 
the  males  are  minute,  long,  narrow,  pure  white,  delicate  structures 
with  a  dorsal  median  longitudinal  furrow.  They  average  about  one 
thirty-second  of  an  inch  in  length.  The  males  may  or  may  not  be 
present  in  large  numbers  among  the  females.  They  are  very  small 
winged  individuals  much  like  those  of  the  brown  apricot  scale  and 
are  of  no  consequence  except  in  fertilizing  the  females.  The  young 
hatch  from  small,  oval  eggs  deposited  beneath  the  shell  of  the  female. 
For  some  days  they  move  about  freely;  with  the  first  moult,  the 
spinning  of  the  shell  begins,  and  with  subsequent  growth  the  legs 
disappear  and  the  insect  becomes  fixed  to  the  bark,  unable  to  move 
farther.  Breeding  continues  throughout  the  spring  and  summer, 
there  being  several  overlapping  generations  a  year. 

This  scale  feeds  only  on  the  bark  of  the  trunk  and  limbs  of  the 
trees  and  hides  under  moss  or  lichens  wherever  an  opportunity  is 
afforded.  It  excretes  no  honey  dew,  and  consequently  smutting  is 
not  associated  with  its  attacks.  In  feeding,  however,  it  causes  pits 
or  depressions  in  the  larger  limbs,  which  may  eventually  crack  or 
become  dead  sunken  areas,  especially  on  old  trees  where  the  insect 
has  occurred  for  many  succeeding  years. 

The  Italian  pear  scale  is  not  widely  distributed  as  an  orchard 
pest,  being  largely  confined  as  such  to  the  Santa  Clara  Valley  and 
adjacent  territory,  although  it  occurs  in  many  other  parts  of  the 
state. 

2  Epidiaspis  piricola  Del  Guercio. 


CIRCULAR  224  CONTROL   OF   SCALE   ON   DECIDUOUS   FRUIT   TREES  3 


Fig.  1. — The  brown  apricot  scale,  Lecanium  corni  Bouche,  on  prune.     Mature 
females. 


4  UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION 

The  chief  host  plants  are  apple,  prune,  pear,  plum,  peach,  currant, 
and  Christmas  berry.  The  apple,  prune,  and  pear  are  the  plants 
most  seriously  attacked. 

The  chief  natural  enemy  is  the  two-stabbed  ladybird  beetle,3  but 
it  is  never  present  in  sufficient  numbers  to  cope  successfully  with 
the  scale. 

SPRAYS4 

The  sprays  most  effective  in  the  control  of  these  two  scale  insects 
are  distillate  emulsions,  crude  oil  emulsions,  and  miscible  oils.  For  the 
brown  apricot  scale  alone,  any  of  these,  if  properly  prepared  and 
applied,  will  give  excellent  results.  The  Italian  pear  scale,  however, 
is  more  resistant  and  requires  heavier  and  more  numerous  applications 
of  distillate  emulsions  and  miscible  oils.  This  scale  yields  most  readily 
to  the  crude  oil  emulsions,  which  are  far  superior  to  commercial  lime- 
sulphur  for  this  purpose. 

Many  growers  realize  the  difficulty  of  securing  proper  materials 
for  homemade  emulsions  as  well  as  the  variability  of  the  homemade 
mixtures  even  under  the  best  conditions.  They  prefer  to  buy  manu- 
factured products,  especially  when  only  small  quantities  are  needed. 
The  commercial  emulsions  and  miscible  oils  are  no  more  effective  than 
a  good  homemade  preparation  and  are  only  of  interest  as  a  matter 
of  convenience.  These  preparations  are  on  the  market  in  great 
variety.  Many  are  sold  under  trade  names.  Practically  all  grades 
of  petroleum  distillates,  as  well  as  crude  petroleum,  are  obtainable  in 
a  form  ready  for  use  after  simple  dilution  with  water.  If  these  ready- 
made  preparations  are  to  be  used,  it  is  important  to  purchase  only 
from  reliable  and  well-known  manufacturers  or  dealers. 


DISTILLATE  EMULSIONS 

Distillate  emulsions  may  be  prepared  at  home  or  purchased  as 
ready-made  commercial  products.  They  are  made  from  fairly  heavy 
distillates   emulsified   with   soap    and    caustic    soda.      A   satisfactory 

3  Chilocorus  bivulnerus  Mulsant. 

4  The  writer  has  purposely  avoided  referring  to  any  specific  brand  of  pro- 
prietary sprays.  Orchardists  may  secure  such  information  from  the  various  local 
and  state  horticultural  officials  and  from  entomologists  and  farm  advisors. 

The  writer  is  indebted  to  Mr.  Geo.  P.  Gray,  chief  of  the  Division  of  Chemistry, 
State  Department  of  Agriculture,  Sacramento,  California,  for  much  of  the  infor- 
mation relative  to  the  composition  and  preparation  of  the  sprays  discussed  in 
this  paper. 


CIRCULAR  224  CONTROL   OF   SCALE   ON   DECIDUOUS   FRUIT   TREES 


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Fig.  2. — The  Italian  pear  scale,  Epidiaspis  piricola  DelGuercio,  on  prune  and 
cherry. 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 


preparation  often  made  and  used  by  orchardists  is  prepared  accord- 
ing to  the  following  formula: 

Distillate   (27°-28°  Baume)  10  gallons 

Caustic  soda  6  pounds 

Liquid  soap  (or  hard  soap  12  pounds)  ....  2  gallons 

Water   to   make 200  gallons 

Directions:  Fill  spray  tank  nearly  full  with  water  and  start 
agitator.  Add  liquid  soap  or  hard  soap  and  caustic  soda  previously 
dissolved  in  small  quantities  of  water.  When  thoroughly  mixed  add 
the  distillate.  This  mixture,  as  well  as  all  the  oil  sprays,  should  be 
constantly  agitated  during  application. 

The  caustic  soda  not  only  aids  in  emulsifying  the  oils,  but  assists 
materially  in  killing  the  moss  on  the  trees.  If  a  commercial  mixture 
is  used,  care  should  be  taken  to  follow  the  directions  on  the  con- 
tainer ;  in  case  proper  results  are  not  obtained,  the  local  Count}^  Horti- 
cultural Commissioner  or  Farm  Advisor  should  be  consulted.  The 
use  of  proprietary  sprays  of  unknown  composition  is  inadvisable. 

MISCIBLE  OILS 

Miscible  oils  are  usually  fairly  heavy  oils  in  which  a  cresol  soap  is 
used  as  an  emulsifying  agent.  Many  of  them  are  proprietary  insecti- 
cides. They  require  more  dilution  than  the  distillate  emulsions.  They 
mix  with  water  readily  and,  if  used  in  proper  proportions,  are  very 
satisfactory.  The  reasons  for  some  poor  results  have  been  traced  to 
recommendations  of  dealers  who  advise  solutions  entirely  too  weak 
to  kill  the  insects. 

CRUDE  OIL  EMULSIONS 

Crude  oil  emulsions  are  made  preferably  from  natural  crude  oil 
coming  directly  from  the  wells.  A  natural  crude  petroleum,  testing 
about  23°  Baume,  is  preferred  as  it  contains  some  of  the  lighter  and 
more  penetrating  oils.  Heavier  crude  oils  have  also  given  satisfactory 
results,  even  those  testing  18°  and  lower. 
Formula  • 

Water   175  gallons 

Liquid  soap  3  gallons 

Natural  crude  petroleum  (21  °-24°  Baume)        25  gallons 

Directions:  Partly  fill  the  spray  tank  with  water,  add  the  liquid 
soap,  agitate  thoroughly  for  one  minute,  add  crude  oil  and  continue 
the  agitation  while  running  in  the  remainder  of  the  water.  If  liquid 
soap  cannot  be  obtained,  use  20  pounds  of  fish-oil  soap  dissolved  in 


Circular  224 


CONTROL  OF  SCALE  ON  DECIDUOUS  FRUIT  TREES 


10  gallons  of  boiling  water  to  which  3  pounds  of  caustic  soda  or  lye 
have  been  added.  To  kill  moss  or  lichens  on  fruit  trees  add  5  pounds 
of  caustic  soda  or  lye  to  the  formula. 

During  the  spraying  operations,  this  emulsion  should  be 
thoroughly  agitated  and  great  care  taken  to  wet  all  of  the  twigs. 
From  8  to  10  gallons  should  be  used  on  a  tree. 

There  are  a  number  of  good  commercial  crude  oil  emulsions  upon 
the  market.     Some  of  them  are  made  from  the  natural  crude  oil,  as 


Fig.  3. — The  Italian  pear  scale,  Epidiaspis  piricola  DelGuereio.     Masses  and 
individual  female  scales. 


are  the  homemade  mixtures,  but  emulsification  is  obtained  by  secret 
artificial  processes  which  render  the  products  stable.  While  crude 
oil  emulsion  sprays  are  annoying  to  the  sprayers  because  of  their 
heavy,  sticky  properties,  they  are  the  most  effective  and  thorough 
of  all  the  oil  sprays.  For  killing  brown  apricot  scale  they  are  no 
better  than  the  distillate  emulsions  and  miscible  oils,  but  for  the 
Italian  pear  scale,  for  moss,  and  for  the  eggs  of  the  red  spider,  they 
are  far  superior.  Injury  may  occur  with  crude  oils  which  are  not 
properly  mixed  or  which  are  composed  of  poor  materials.  If  there 
is  a  quantity  of  free  crude  oil  on  top  of  the  material  in  the  spray  tank 
more  soap  or  caustic  soda  should  be  used ;  if  a  heavy  scum  or  residue 
remains  in  the  tank,  relief  may  be  obtained  by  thinning  down  the 


8  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION 

crude  oil  with  distillate  or  kerosene.  When  crude  oil  is  thoroughly 
applied,  it  sometimes  penetrates  the  fruit  buds  to  a  considerable 
extent.  Some  of  these  may  be  injured  and  even  killed,  but  most  of 
the  buds  are  not  injured.  Buds  may  be  killed  also  by  applying  the 
free  oil  or  residue  referred  to  above. 

All  these  oil  sprays  and  particularly  the  crude  oil  emulsions  hasten 
the  blooming  period  of  the  trees  from  one  to  three  weeks.  Crude  oil 
emulsion  has  also  partially  controlled  the  brown  rot  fungus5  which 
attacks  apricot  and  prune  trees  in  the  Santa  Clara  Valley.  The  crude 
oil  emulsions  originated  in  the  Santa  Clara  Valley  and  are  rarely 
found  elsewhere,  though  they  have  been  in  use  there  for  the  past  five 
or  six  years.  Through  the  manufacturers,  however,  their  sale  is  being 
pushed  in  other  parts  of  California  and  in  many  other  states,  and 
their  worth  is  gradually  becoming  known  and  appreciated. 

The  brown  apricot  scale  is  effectually  controlled  by  applications 
of  crude  oil  emulsions  used  for  the  Italian  pear  scale,  but  the  latter 
cannot  be  killed  by  the  ordinary  applications  of  distillate  emulsions 
and  miscible  oils  unless  thorough  and  repeated  treatments  are  given. 

APPLICATION    OF    SPRAYS 

Orchardists  have  much  to  learn  regarding  the  application  of 
sprays,  particularly  as  to  the  best  kind  of  nozzle.  In  most  cases  where 
poor  nozzles  are  used,  the  work  is  done  by  hired  help  generally  not 
conversant  with  the  best  types  of  spraying  equipment.  The  use  of 
the  single  Bordeaux  nozzle  on  an  extension  rod  is  common  in  many 
parts  of  the  state.  As  an  advance  step  over  this  we  occasionally  find 
one  and  sometimes  two  good,  large  cyclone  nozzles  on  a  rod.  The  use 
of  a  rod  thus  equipped  considerably  lessens  the  time  consumed  in  the 
application.  The  advent  of  the  spray  gun  is  a  very  important  step 
in  spraying  operations. 

The  chief  advantages  of  the  spray  gun  are: 

It  greatly  reduces  the  weight  to  be  carried  by  the  operator  and 
makes  the  work  of  spraying  less  objectionable. 

By  reason  of  its  light  weight  it  can  be  more  quickly  operated. 

It  affords  an  adjustable  spray  for  all  kinds  of  work. 

It  is  easily  and  quickly  cut  off  when  going  from  tree  to  tree. 

Any  stoppage  of  the  nozzle  can  be  dislodged  by  a  slight  adjust- 
ment. 

It  throws  a  greater  volume  of  material,  practically  doubling  the 
efficiency  of  each  operator  handling  a  line  of  hose,  thereby  saving 
time  and  labor. 


5  Sclerotinia  cinerea  (Bon.)   Wor. ;  previously  known  as  Sclerotinia  fructigena 
(Pers.)   Sch.     Synonymy  by  Professor  W.  T.  Home. 


CIRCULAR  224  CONTROL   OF   SCALE   ON   DECIDUOUS   FRUIT   TREES 


Fig.  4. — Portion  of  a  limb  from  pear  tree  showing  deformation  due  to  the 
continued  work  of  the  Italian  pear  scale,  Epidiaspis  piricola  DelGuercio. 


10  UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION 

There  are  many  tj^pes  of  spray  guns.  In  making  a  purchase  the 
capacity  of  the  spraying  machine  must  be  taken  into  account,  for 
this  will  determine  whether  a  gun  of  small  or  large  throwing  capacity 
should  be  used,  or  whether  one  or  two  should  be  operated  on  the 
machine.  A  pressure  of  at  least  200  pounds  should  be  maintained 
at  all  times.  If  the  machine  will  not  carry  this  with  one  gun,  spray 
rods  must  be  resorted  to  in  order  to  get  the  best  results. 

It  is  true  that  in  the  beginning  one  is  likely  to  use  more  material 
with  a  spray  gun,  but  the  ease  of  operation  and  saving  in  time  and 
labor  much  more  than  offset  this  objection.  The  value  of  the  spray 
gun  for  many  kinds  of  spraying  work  has  been  proved  and  its  popu- 
larity is  fully  warranted.  It  is  particularly  valuable  for  the  control 
of  the  brown  apricot  scale,  which  is  usually  located  on  the  underside 
of  the  twigs  of  the  current  year's  growth  where  it  is  readily  hit;  and 
also  for  the  control  of  the  Italian  pear  scale  located  upon  the  trunks 
and  larger  limbs  where  a  thorough  drenching  with  a  strong,  coarse 
spray  is  necessary. 

In  spraying  for  the  brown  apricot  scale,  care  must  be  taken  to 
cover  all  of  the  tips  of  the  small  twigs  around  the  edges  and  tops  of 
the  trees  where  the  young  insects  are  located  upon  the  new  growth. 


TIME   TO    SPRAY 

Both  the  brown  apricot  scale  and  the  Italian  pear  scale  can  be 
controlled  best  by  spraying  between  December  15  and  February  15. 
During  that  time  the  trees  are  absolutely  dormant  and  safe  from 
spray  injury.  Application  may  be  made  as  late  as  the  starting  of 
the  buds,  but  great  care  must  be  exercised  in  late  spraying  to  avoid 
injuring  the  blossoms.  While  injury  does  not  always  result  from 
applications  made  when  the  trees  are  in  full  bloom,  applications  are 
dangerous  at  this  time  and  the  spraying  should  be  finished  before  the 
danger  point  arrives. 

DANGERS    IN    USING    OIL    SPRAYS 

Under  ordinary  field  conditions  in  California  there  is  little  danger 
in  the  use  of  oil  sprays,  but  it  is  advisable  to  call  attention  to  a  few 
important  points  which  should  not  be  lost  sight  of  by  orchardists. 

1.  Do  not  use  improper  mixtures.  If  the  emulsions  of  crude  oils 
fail  to  mix  readily  with  water,  and  much  free  oil  rises  to  the  surface, 
or  a  heavy  residue  remains  after  the  spray  tank  has  been  emptied, 
suspend  operations  and  consult  spray  manufacturers,  local  County 


CIRCULAR  224  CONTROL   OF   SCALE    ON   DECIDUOUS   FRUIT    TREES  11 


Horticultural  Commissioner  or  Farm  Advisor  as  to  proper  procedure 
in  remedying  the  product  or  in  securing  a  reliable  new  one. 

2.  Do  not  apply  oil  sprays  except  when  the  trees  are  dormant.  As 
already  pointed  out,  injury  may  result  from  applying  sprays  when 
the  buds  begin  to  open  in  the  spring  due  to  the  penetration  of  the 
sprays  into  the  tender  tissues  of  the  buds.  Injury  may  also  occur 
in  the  fall  if  spraying  is  begun  too  earty,  as  well  as  in  the  spring  if 
done  too  late,.     The  trees  are  most  resistant  to  spray  injury  from 


Fig.  5. — Two  common  types  of  spray  guns  used  in  modern  spraying  operations. 

December  15  to  February  15  when  the  buds  are  thoroughly  protected 
by  the  closely  adhering  bud  scales.  Oil  sprays  have  frequently  been 
applied  without  apparent  injury  when  the  trees  are  in  full  bloom, 
but  such  a  practice  is  attended  with  great  danger  and  the  possibility 
of  losing  the  entire  crop. 

3.  Do  not  spray  when  the  trees  are  in  need  of  water.  During  late 
dry  seasons  much  injury  may  result  in  using  oil  sprays  if  the  trees 
need  water.  The  use  of  oils,  and  in  fact  of  all  other  sprays,  should 
be  delayed  until  after  rain  or  irrigation. 

Also  avoid  spraying  after  a  continued  spell  of  dry  winds,  for 
these  so  deplete  the  moisture  in  the  bark  of  the  trees  as  to  permit 
penetration  of  the  sprays  from  which  severe  injury  to  the  bark  and 
buds  may  result. 


